It looks to me like QuickCheck is not managing to generate any acceptable arguments for the tests. Could you post your Arbitrary instance for Decimal? But then it is odd that QuickCheck manages to find a counterexample when running under HSpec. Could you post the HSpec output?
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dave4420Feb 27 '13 at 9:38

2 Answers
2

The likely problem here is that QuickCheck is giving up after finding too many unsuitable test cases. Raising topt_maximum_unsuitable_generated_tests will give QuickCheck more opportunities to find acceptable cases and allow the test to finish.